This invention relates to contacts for circuit breakers, and, more particularly, relates to the interrelationship between a movable contact and a stationary contact within a circuit breaker.
U.S. Pat. No. 4,616,198 entitled xe2x80x9cContact Arrangement for a Current Limiting Circuit Breakerxe2x80x9d describes the early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let-through upon the occurrence of an overcurrent condition.
When the contact pairs are arranged upon one movable contact arm such as described within U.S. Pat. No. 4,910,485 entitled xe2x80x9cMultiple Circuit Breaker with Double Break Rotary Contactxe2x80x9d, some means must be provided to insure that the opposing contact pairs exhibit the same contact pressure to reduce contact wear and erosion.
One arrangement for providing uniform contact wear is described within U.S. Pat. No. 4,649,247 entitled xe2x80x9cContact Assembly for Low-voltage Circuit Breakers with a Two-Arm Contact Leverxe2x80x9d. This arrangement includes an elongate slot formed perpendicular to the contact travel to provide uniform contact closure force on both pairs of contacts.
State of the art circuit breakers employing a rotary contact arrangement employ a rotor assembly and pair of powerful expansion springs to maintain contact between the rotor assembly and the rotary contact arm as well as to maintain good electrical connection between the contacts. The added compression forces provided by the powerful expansion springs must be overcome when the contacts become separated by the so-called xe2x80x9cpopping forcexe2x80x9d of magnetic repulsion that occurs upon over-current conditions to momentarily separate the circuit breaker contacts within the protected circuit before the circuit breaker operating mechanism has time to respond.
The thickness of the moveable contact arm as well as the size of the contact springs has heretofore been increased to proportionately increase the overcurrent level at which the popping force causes the contacts to become separated. However, increased thickness and size decreases contact arm mobility and increases the cost.
In an exemplary embodiment of the present invention, a pair of opposed contacts for use in a circuit breaker comprises a first contact having a first contact face and a second contact face, the first contact face and the second contact face forming an angle A between 0 and 180 degrees. The pair further includes a second contact having a third contact face and a fourth contact face, the third contact face and the fourth contact face forming a reflex angle B between 180 and 360 degrees. A sum of angle A plus angle B is substantially 360 degrees so that the first contact and the second contact can lie flushly together.